It is generally known that manual and automatic transmissions usually comprise an input shaft, an output shaft that is coaxial to the input shaft and a countershaft. Depending on the number of gears, there is a corresponding number of gear wheels on the gear shafts, on which there is a stationary wheel mounted on a gear shaft combs with at least one loose wheel arranged on a further gear shaft.
With a forward shift generally one of the loose wheels will be non-rotatably connected to the gear shaft via a positively acting clutch arrangement, which transmits the total drive torque. In order to transmit large torque with simple, space-saving and easily switched means, one preferably uses positive clutches. During the forward gearshift the tractive power of the driving engine will, however, be interrupted by way of a special switching and starting clutch.
In order to shift such transmissions easily, lightly, jerk-free, quickly and with low noise, the switching parts of the clutch arrangement must have about the same number of revolutions before these mesh with one another. For this purpose, synchronizing parts are provided, which delay or accelerate the drive-side part of the drive train between the shifting and starting clutch and clutch arrangement that is supposed to be shifted during a tractive power interruption phase to a speed that is set depending on the driving speed and the gear ratio of the target gear. If one switches from a lower gear to a higher gear then with the help of the synchronization arrangement the drive-side part of the gearbox will be delayed, whereas it will be accelerated in a reverse gear motion.
The ordinary synchronization arrangements have for these delayed and accelerated actions, friction clutches in the form of friction cones. These do not have to transmit the entire torque, but only perform the synchronization work, which is a result of the moments of inertia of the rotating masses of the drive-side part of the transmission as well as the friction-related drag torque. Therefore they can accordingly be made of a small dimension.
Typically each of the positive clutch arrangements is provided with a synchronization arrangement. It is, however, also possible that a central synchronization arrangement assumes the synchronizing work for several or all positive clutch arrangements.
In order to relieve the driver of a vehicle from the mechanical shift and clutch processes associated with shifting operations, these automated shifting processes are performed by auxiliary force-aided adjusting controls in automated gearboxes, which are selected by a controlling and regulation arrangement.
In addition, such a controlling and regulation arrangement uses vehicle sensor data to detect the driver's preferences and controls and regulates the switching activity of the gearbox on their basis by way of memorized controlling and regulation programs.
In such automatic gearboxes, the synchronization process can, for example, be controlled and regulated so that during reverse control operations the number of rotations of the gear input shaft or the countershaft will be raised due to the increase in the engine speed whereas during up-shifts these drive-side shafts of the gearbox will be decelerated. In order to carry out such brake activities, there are centrally synchronized gearboxes, which usually are coupled via a gearbox brake that is connected to the counter shaft. Such gearbox brakes can be operated electrically, hydraulically or pneumatically, whereby the latter operating mechanism is more often used for commercial vehicle gearboxes.
In DE 196 52 916 A1 an automatic transmission with a hydraulically or pneumatically operated gearbox brake is known wherein on the latter a countershaft can act. The pressure fluid control valves of the gearbox brake are controlled by a microprocessor dependent on the desired type of switch and the other driving conditions.
If a higher gear is, for example, chosen and the countershaft must be decelerated for synchronization, the microprocessor will calculate a target revolution speed (synchronized revolution speed) for the countershaft based on the chosen gear transmission ratio and by way of a sensor, wherein mechanic coupling of the target gear loose wheel can occur when said target speed has been reached.
Due to the usually difficult to regulate air pressure as well as other varying surrounding conditions, the brake power of the gearbox brake is subjected to large fluctuations. In order to achieve the necessary rotation speed, that is the maximum distance of the actual rotation speed of the gear input shaft or that of a countershaft driven by it to the target rotation speed for the concrete switch activity, according to the state of the art, the braking gradient is determined and taken into consideration by the microprocessor during the control of the gearbox brake. For this to happen, the microprocessor regulates the control valves in such a way that the known preset given values and thus the synchronized rotation speed for engagement of the clutch arrangement on the respective loose wheel can be reached.
Unfortunately, the synchronous rotation speed is not a set speed for a switch activity and is among other things dependent on the grade of the road. The reason for this is that a switch activity with an open starting and switching clutch as well as a grade can lead to a negative vehicle acceleration and thus to a decline in the gear output speed and for a gradient when the gearbox brake is not being operated it could lead to a positive vehicle acceleration. These influences have not been accounted for previously in the state of the art for the control and regulation methods for gearbox brakes, which means that before their means of operation was not complete.
The task of the invention is therefore to continue to improve the control and regulation of the gearbox brake.
The solution to this task is found in the features of the main claim, while the inventive advantages of further development and design are found in the subordinate claims.